1. Field of the Invention
The present invention is directed to partially and fully implantable hearing systems for rehabilitation of a pure sensorineural hearing loss or combined conduction and inner ear hearing loss with mechanical stimulation of the impaired ear.
2. Description of Related Art
Recently, partially and fully implantable hearing aids for rehabilitation of a pure inner ear hearing disorder or combined sound conduction and inner ear hearing disorder with mechanical stimulation of the damaged ear have become available on the market or will soon be available (journal HNO 46:844-852, 10-1998, H. P. Zenner et al., xe2x80x9cInitial implantations of a completely implantable electronic hearing system in patients with an inner ear hearing disorderxe2x80x9d; journal HNO 46:853-863, 10-1998, H. Leysieffer et al., xe2x80x9cA completely implantable hearing system for inner ear hearing handicapped: TICA LZ 3001xe2x80x9d; U.S. Pat. Nos. 5,277,694; 5,788,711; 5,814, 095; 5,554,096; and 5,624,376). Especially in fully implantable systems, is the visibility of the system not an issue, so that in addition to the advantages of high sound quality, the open auditory canal and full suitability for everyday use, high future patient acceptance can be assumed. Basically, in these implantable systems, the output signal is a mechanical vibratory stimulus which directly excites the middle ear or inner ear. The coupling of the mechanical excitation which is produced by an electromechanical transducer takes place by direct mechanical connection of the vibrating transducer element to the ossicle chain or an ossicle of the middle ear or to the inner ear (commonly assigned U.S. patent application Ser. No. 09/042,805) or by force coupling via an air gap in, for example, electromagnetic transducers.
The coupling quality of the mechanical excitation is influenced by many parameters and contributes significantly to rehabilitation of hearing loss and to the perceived hearing quality. Intraoperatively, this quality of coupling can only be assessed with difficulty or not at all, since the amplitudes of motion of the vibrating parts even at the highest stimulation levels are in a range around or far below 1 xcexcm , and therefore, they cannot be assessed by direct visual inspection. Even as this is done using other technical measurement methods, for example, by intraoperative laser measurements (for example, laser doppler vibrometry), the uncertainty of a long-term stable, reliable coupling remains, since this can be adversely affected among others by necrosis formation, tissue regeneration, air pressure changes and other external and internal actions. In particular, in completely implantable systems, it remains necessary to be able to assess the coupling quality of the transducer, since in a full implant, it is not possible to separately measure individual system components at their technical interfaces if, for example, the implant wearer complains of inferior transmission quality which cannot be improved by reprogramming of individual audiologic adaptation parameters, and therefore, surgical intervention to improve the situation cannot be precluded. Even if this is not the case, there is fundamental scientific interest in having available a reliable monitor function of long term development of the quality of the transducer coupling.
International Patent Application Document WO 98/36711 proposes a method for this purpose which works with objective audiometric methods such as, for example, ERA (electric response audiometry), ABR (auditory brainstem response) or electrocochleography in partially and fully implantable systems with mechanical or electrical stimulation of the impaired or failed hearing. By electrical tapping via external head electrodes or implanted electrodes, stimulus responses which are evoked by application of suitable stimulating effects are objectively determined. The advantage of this method lies in that intraoperatively objective data of transmission quality can be obtained under full anesthesia. However, the major disadvantage, among others, is that these objective audiometric methods can only be of a qualitative nature, delivering essentially only data at the auditory threshold and/or only to a limited extent above threshold, and in particular, have only inadequate quantitative accuracy in frequency specific measurements. The subjective evaluation of transmission quality and subjective audiologic measurements in the range above threshold as, for example, loudness scales are not possible.
The primary object of this invention is to devise a partially or fully implantable hearing system which makes it possible, while circumventing these defects by psychoacoustic measurements, i.e, by subjective patient responses, to determine the coupling quality of the electromechanical transducer to the middle or inner ear without other biological-technical interfaces having been incorporated into the evaluation which adversely effect the reliability of the determination of transducer coupling quality.
Proceeding from a partially and fully implantable hearing system for rehabilitation of a pure sensorineural hearing loss or combined conduction and inner ear impairment with a microphone which delivers an audio signal, an electronic signal processing and amplification unit which is located in an audio signal processing electronic hearing system path, an implantable electromechanical output transducer and a unit for power supply of the implant, this object is achieved in accordance with the invention by an electronic audiometer unit being added to the hearing system and generating the audiometry signals for an audiologic, subjective study and evaluation of the coupling quality of the electromechanical output transducer and feeding it into the audio signal processing path of the hearing implant.
The audiometer module preferably is formed of one or more electronic signal generators which can be adjusted or programmed from the outside and which feed an electrical audiometry signal into the signal processing path of the implant. The electromechanical output transducer of the implanted hearing system becomes technically reproducible by the audiometer module and is directly triggered electrically in a quantitatively determined manner; in this way, adulteration of the stimulation level is prevented, as can occur, for example, by headphone and especially acoustic free field presentation of the audiometric test sound because, here, the sensor or microphone function with all pertinent variabilities is incorporated into the psychoacoustic measurement.
The system in accordance with the invention has the advantage, among others, that, for example, frequency-specific auditory threshold measurements with pure sinusoidal tones or narrowband signals (for example, third octave noise) can be very easily reproduced at longer study time intervals. Furthermore, the acquisition of reproducible psychoacoustic data in the supraliminal area, for example, loudness scalings, is also possible. In addition, by offering pure signals such as, for example, sinusoidal signals, nonlinearities can also be subjectively interrogated which can arise, for example, by diminishing coupling quality. These studies are possible only to a limited extent or not at all by the objective measurement methods described at the beginning on the basis of evoked potentials.
Basically, in the fully implantable systems, the approach according to the invention yields the advantage that the parameters of signaling such as, for example, the electrical operating level of the electromechanical implant transducer are quantitatively exactly determined and can be reproduced by the generators within the implant and are not subject to fluctuations, as occur, for example, in a full implant by acoustic headphone presentation of the test signals. In this last case, the transmission function of the implanted acoustic sensor (microphone) is incorporated into transmission at the same time. The sensor function can also be subject to time fluctuations and thus makes an exact interface definition for the output transducer transfer function impossible.
As the implantable electromechanical output transducer, especially a transducer as per U.S. Pat. No. 5,277,694 is suitable, i.e., a transducer in which one wall of the transducer housing is made as a vibratory membrane which together with a piezoelectric ceramic disk applied to the membrane inside, represents an electromechanically active heteromorphic composite element.
Another transducer design suitable for these purposes is described in commonly assigned U.S. patent application Ser. No. 09/097,710. It is a transducer arrangement for partially or fully implantable hearing aids for direct mechanical stimulation of the middle ear or inner ear, which is provided with a housing which can be fixed at the implantation site with respect to the skull and with a mechanically stiff coupling element which can move relative to the housing, the housing containing an electromechanical transducer with which the coupling element can be caused to vibrate; these vibrations are transmitted to the middle ear ossicle or directly to the inner ear after completed implantation of the transducer arrangement. The electromechanical transducer is made as an electromagnet arrangement which has a component which is fixed relative to the transducer housing, especially a ring coil, and a vibratory component, preferably in the form of a permanent magnetic pin which dips into the center opening of the ring coil and which is connected to the coupling element, such that the vibrations of the vibratory component are transmitted to the coupling element.
But, a transducer of the type described in commonly assigned U.S. patent application Ser. No. 09/311,563 is also advantageous. It is a transducer for partially or fully implantable hearing aids for direct mechanical excitation of the middle ear or inner ear which is provided with a housing which can be fixed at the implantation site and with a mechanically stiff coupling element which can move relative to the housing, the housing containing a piezoelectric transducer with which the coupling element can be caused to vibrate, these vibrations are transmitted to the middle ear ossicle or directly to the inner ear after completed implantation of the transducer. Furthermore, in the housing there is an electromagnet arrangement which has a component which is fixed relative to the housing and has a vibratory component which is connected to the coupling element such that the vibrations of the vibratory component are transmitted to the coupling element. This transducer has the advantage that the frequency response of the transducer can be improved, both compared to purely piezoelectric and purely electromagnetic systems, so that an adequate hearing impression at a sufficient loudness level is enabled. In particular, a largely flat frequency response of the deflection of the coupling element can be implemented in a wide frequency band at a sufficiently high stimulation level and low power consumption.
In the hearing system of the invention, preferably, patient-specific signal parameters for the audiometry function can be individually adapted to the requirements and pathological requirements of the patient by means of an electronic unit.
The electronic signal processing and amplification unit can have an amplifier downstream of the microphone, an audiologic signal processing stage supplied with the output signal of the amplifier and a driver amplifier upstream of the electromechanical output transducer. Advantageously, the electronic module can be provided with a signal generator arrangement for generating the signals necessary for the audiometry function and a summing element connected between the signal processing stage and the driver amplifier and via which both the output signal of the audiologic signal processing stage and also the output signal of the signal generator arrangement pass to the driver amplifier.
However, according to one modified embodiment of the invention, there can also be a digital signal processor as the audiological signal processing stage which is designed both for processing of the audio signal and also for generating the signals necessary for the audiometry function and for combining the latter signals with the audio signal. In this case, an analog to digital converter can be connected upstream of the signal processor and a digital to analog converter downstream of the signal processor.
The digital to analog converter and the driver amplifier can be combined in one module.
The signal processor is preferably equipped with a data storage for storing the patient-specific, audiologic adaptation parameters and/or parameters for generating the signals for the audiometry function.
To control at least a part and preferably all of the signal processing and/or generating stages there can advantageously be a microcontroller which has a data storage for storing patient-specific, audiologic adaptation parameters and/or the operating parameters of the signal generator arrangement.
However, the signal processor can also be designed itself for controlling at least one part and preferably all of the signal processing and/or generating stages.
For data input into the data storage, a telemetry unit is suitable which communicates by wire or wirelessly with an external programming system.
If the hearing aid is made to be fully implantable, preferably the signal processing and amplification unit which is in the electronic hearing system path, the electronic module for generating and feeding the signals necessary for the audiometry function and the telemetry unit as the electronic module are housed, together with the power supply unit, in a hermetically sealed and biocompatible implant housing. Here, the electronic module is advantageously connected via an implant line to a microphone which can be implanted subcutaneously in the posterior wall of the auditory canal and via an implantable line to the electromechanical output transducer. This connection can be made permanent or detachable. For a detachable connection, especially a plug-in connection as is described in particular in U.S. Pat. No. 5,755,743 is suitable. One such connection arrangement has at least a first contact, at least one second contact supported on an elastic body and a sealing mechanism for causing the face of the first contact to engage the face of the second contact, the first contact being surrounded by at least one sealing crosspiece which is pressed into the elastic body when the contacts engage and seals the contacts to the outside.
The output transducer can be coupled, preferably, via a coupling element to an ossicle of the middle ear chain for transmission of the output-side mechanical transducer vibrations.
Especially, the approaches of the type described in U.S. Pat. No. 5,277,694 and commonly assigned U.S. patent application Ser. No. 09/042,805 are suitable for this purpose. Here, advantageously, an actively vibratory part of the output transducer can be joined mechanically securely to a connecting rod which is coupled via a coupling element to part of the ossicle chain. To adjust the relative location of the connecting rod and coupling element and to fix these elements in the set relative position, the coupling element is preferably made sleeve-shaped at least in the fixing area and it can be plastically cold-deformed by means of a crimping tool, while the connecting rod is made bar-shaped at least in the fixing area, provided with a rough surface, and under the influence of the crimping force applied with the crimping tool, it cannot be plastically cold-deformed, in the fixed state, the sleeve-shaped part of the coupling element deformed by cold flow being attached permanently and without play on the bar-shaped part of the connecting rod. However, the end of the connecting rod away from the output transducer can also be inserted into a hole of a part of the ossicle chain and fixed there.
Furthermore, the output transducer can also be designed such that it can be coupled via an air gap to the ossicle chain or the inner ear, as is described in particular in U.S. Pat. No. 5,015,225.
A fully implantable hearing aid, in another embodiment of the invention, includes an external system for transcutaneous transfer of patient-specific hearing aid and audiometry programming data to the implant-side telemetry unit.
As the power supply unit in particular, a primary battery or a secondary, rechargeable element, i.e., a rechargeable battery, can be considered. In the latter case, the telemetry unit is additionally made, preferably, as a power receiving circuit for implant-side availability of recharging energy for the power supply unit, while the external system is at the same time built as a charger. In particular a charging system of the type known from U.S. Pat. No. 5,279,292 or arrangements as are described in commonly assigned U.S. patent applications Ser. Nos. 09/311,565 and 09/311,566are suitable for this purpose.
It is also possible for a portable remote control unit to be provided for setting or changing the hearing aid or audiometry functions.
In a partially implantable system, an implant part preferably has, in addition to the output transducer, a power and signal receiving interface and an electronic system connected between the receiving interface and the output transducer, with the components necessary for power supply and data regeneration, and an external system part comprises the microphone, an electronic module with the signal processing unit in the hearing aid path and the electronic module necessary for generation and feed of the signals necessary for the audiometry function, a driver unit and a power and signal transmitting interface connected to the output of the driver unit.
Furthermore, the partially implantable hearing system preferably includes an external system for transfer of patient-specific hearing aid and audiometry programming data to the electronic module of the external system part.
In the following, advantageous embodiments of the invention are explained using the drawings.